一个液压系统压力低时:().
A.主警告灯亮
B.主警告灯亮且“叮”的一声
C.无警告
参考答案:B
E-mail, as well as telephones, ______ an important part in daily communication.
A.is playing
B.have played
C.are playing
D.play
“以知识为本”使教育异化为记忆和训练内容。